Musket son brought into passenger vehicle by mistake (11)
I believe the answer is:
blunderbuss
'musket' is the definition.
(blunderbuss is a kind of musket)
'son brought into passenger vehicle by mistake' is the wordplay.
'son' becomes 's'.
'brought into' means one lot of letters goes inside another.
'passenger vehicle' becomes 'bus' (I've seen this before).
'by' says to put letters next to each other.
'mistake' becomes 'blunder' (blundering is a kind of mistaking**).
's' going into 'bus' is 'buss'.
'buss' put after 'blunder' is 'BLUNDERBUSS'.
(Other definitions for blunderbuss that I've seen before include "Old musket" , "Short large-bore musket with flared muzzle" , "Weapon" , "Early form of gun" , "one was fired" .)